Diarrhea: Causes, Symptoms and Treatments


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Diarrhea is a problem everyone is familiar with – it is one of the most common reasons for people to seek medical advice1 – but it can range from being a mild, usually temporary condition, to one that can threaten life.

It is estimated that there are 2 billion cases of diarrheal disease every year globally, and that 1.9 million children below the age of 5 years, mostly in developing countries, die annually.2

The British English for diarrhea is diarrhoea.

Diarrhea should not be confused with the frequent passing of stools of normal consistency – this is not diarrhea. Diarrhea is instead characterized by abnormally loose or watery stools.3

Similarly, breastfed babies often pass loose, pasty stools, which is normal and not diarrhea.3

Contents of this article:

  1. How is diarrhea classified?
  2. Causes of diarrhea
  3. Symptoms of diarrhea
  4. Tests and diagnosis
  5. Treatments for diarrhea
  6. Diarrhea prevention

You will also see introductions at the end of some sections to any recent developments that have been covered by MNT‘s news stories. Also look out for links to information about related conditions.

Fast facts on diarrhea

Here are some key points about diarrhea. More detail and supporting information is in the body of this article.

  • Diarrhea is unusually loose or watery stools.
  • The problem may be acute, persistent or chronic.
  • Most cases are caused by infection with bacteria, viruses or parasites.
  • So-called “functional” chronic diarrhea includes irritable bowel syndrome (IBS).
  • Inflammatory bowel diseases (IBD) are causes of chronic diarrhea, including Crohn’s disease and ulcerative colitis.
  • Diagnosis is usually made clinically – that is, after a doctor “takes and history” and completes an examination.
  • Further tests – including on a stool sample – may be appropriate in some cases.
  • The priority of treatment is to correct dehydration with fluids and electrolytes.
  • Antidiarrheal medications can reduce diarrheal output. Zinc supplement is effective in children.
  • Nutritional and probiotic interventions can be tried against diarrhea.

How is diarrhea classified?

There are three forms of diarrhea defined by the length of time that the condition lasts:1,2,4

[man with stomach cramps]

  • Acute diarrhea is short-lasting – between several hours and a number of days, and for less than 2 weeks or 14 days. World guidelines further say that acute diarrhea is the presence of 3 or more abnormally loose or watery stools in the preceding 24 hours. Acute diarrhea includes cholera. If the acute diarrhea is bloody, it is called dysentery
  • Persistent diarrhea lasts for longer than 2 weeks but less than 4 weeks
  • Chronic diarrhea lasts more than 4 weeks.

Most people think of diarrhea in terms of stool consistency – how watery it is. This may be the best concept also recognized by clinicians, who additionally define it in terms of stool frequency, consistency, volume or weight.5

For example, some definitions cite a daily stool weight greater than 200 grams a day – but there can be great variety between different people’s normal bowel motions.5

Perhaps the simplest definition of diarrhea is the passage of loose stools more frequently than is usual for the individual.4

The pathophysiology of diarrhea further defines it. There are four mechanisms by which the condition occurs, and there can be overlap between these in individual cases:1

  • Osmotic diarrhea occurs when the small intestine cannot absorb a soluble compound and fluid is drawn into the gut
  • Secretory diarrhea results from active chloride secretion into the bowel. Water follows the chloride ions, leading to a net loss of fluid
  • Inflammation of the intestinal lining
  • Motility of the intestines is increased.

Causes of diarrhea

Most cases of diarrhea are the symptom of an infection in the gastrointestinal tract.4

The microbes causing gastrointestinal infection that leads to diarrhea include:4

  • Bacteria
  • Viruses
  • Parasitic organisms.

The most commonly identified causes of acute diarrhea in the US are the bacteria Salmonella, Campylobacter, Shigella and Shiga toxin-producing Escherichia coli.6

There are cases of chronic diarrhea that are labeled “functional” because they cannot be not explained by structural or biochemical abnormalities.7

In the developed world, irritable bowel syndrome (IBS) is the most common cause of functional diarrhea.7,8

IBS is a complex of symptoms usually diagnosed by a process of elimination of other possible problems. There is cramping abdominal pain and altered bowel habit, either with diarrhea or constipation.7,8

Inflammatory bowel disease (IBD) is another cause of chronic diarrhea, in which case the diagnosis will be either ulcerative colitis or Crohn’s disease, and there is often blood and pus in the stool in both conditions.8

Other major causes of chronic diarrhea include:8

  • Microscopic colitis – this is secretory diarrhea usually affecting older people. There is microscopic inflammation, with changes visible on microscopy of a colon biopsy. The persistent diarrhea is often during the night
  • Malabsorptive and maldigestive diarrhea – the first is caused by impaired nutrient absorption, the second by impaired digestive function. Celiac disease is one example
  • Chronic infections – these diarrheas are persistent whereas most infectious causes lead to acute diarrhea. A history of travel or antibiotic use are clues, and numerous bacteria and parasites are culprits. These cases are primarily inflammatory, although malabsorption is caused by giardiasis, a parasitic infection
  • Drug-induced diarrhea – the obvious cause is laxatives, but a list of other drugs also leads to diarrhea – check medications with a pharmacist or doctor
  • Endocrine causes – chronic secretory diarrhea can have a range of hormone system causes, including Addison disease, carcinoid tumors. Meanwhile, hyperthyroidism can increase gut motility
  • Cancer causes – neoplastic diarrhea is associated with a number of gut cancers.

On the next page we look at the symptoms of diarrhea and how diarrhea is diagnosed. On the final page we discuss the available treatments and ways in which to prevent diarrhea.


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Symptoms of diarrhea

Diarrhea is itself a symptom – of frequent and loose or watery stools. It may be accompanied by other symptoms as a result, including the following:9

  • Stomach pain
  • Abdominal cramps
  • Bloating
  • Thirst
  • Weight loss
  • Fever.

Some symptoms are considered red flags for more serious illness – blood or pus, fever, signs of dehydration, persistent vomiting, chronic diarrhea or weight loss – learn more about this in the next section covering diagnosis.1,10

Tests and diagnosis of diarrhea

Doctors start by “taking a history” – asking questions about the problem, including about medicines received, past medical history and underlying conditions.2

Also established initially are:2,6

  • When the problem started
  • Stool frequency, type (for example, watery, mucus-filled, pussy) and volume
  • Whether blood is present in the stool
  • Whether there has been vomiting.

Doctors will also be concerned about whether there is dehydration, and if so, its severity – the greatest danger to life with diarrhea is created by dehydration, which has three stages:1,4

  • Early dehydration, which shows no signs or symptoms, or possibly lightheadedness and lassitude (lack of energy)
  • Moderate dehydration – signs of this are thirst, restlessness or irritability, dizziness, reduced elasticity of the skin, pinched face, dry tongue and sunken eyes
  • Severe dehydration – signs of this are increased severity of the above, and shock, with reduced consciousness, low urine output, cool, moist extremities, a rapid and feeble pulse, low or undetectable blood pressure, and pale skin; a coma can ensue.

Death may follow severe dehydration if treatment with rehydration therapy is not instituted urgently.4

Tests for diarrhea

Because most cases of diarrhea are self-limiting and resolve themselves, and because the diagnosis can be made clinically, tests are not usually required. But in more severe cases, for example, doctors may order further testing.6

Acute cases, particularly if the patient is very young or old, that may require a stool sample to be tested (with microscopy, culture, fecal leukocyte testing, and, if recent antibiotics, Clostridium difficile testing) include:1,10

Parasites or their eggs can be seen under a microscope.

  • Those showing signs of fever or dehydration
  • Having bloody or pussy stools
  • With severe pain
  • Low blood pressure
  • The person is immunocompromised
  • There has been recent foreign travel to places outside western Europe, North America, Australia and New Zealand
  • The person has recently received antibiotics or been in hospital
  • Diarrhea persisting for more than one week.

Microscopy will evaluate the sample for parasites or their eggs.11

A bacterial infection may cause white blood cells to appear in the stool, so WBC is tested in a sample. And a culture of the stool can check for pathogenic gastrointestinal bacteria.11

There is a rapid test for Clostridium difficile toxin to pick up this bacterial infection, and labs can provide a number of other tests of the stool for numerous pathogens.11

Blood tests will also be needed for these patients to measure CBC (complete blood count) and electrolytes, BUN (blood urea nitrogen) and creatinine.

Chronic cases of diarrhea will be tested according to the suspected underlying cause, and may include these investigations:1

  • Full blood count – for anemia or a raised platelet count suggesting inflammation
  • Liver function tests, including albumin level
  • Tests for malabsorption – calcium, vitamin B12 and red blood cell folate, iron status (ferritin), thyroid function tests
  • ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein) – with raised levels possibly pointing to inflammatory bowel disease (IBD)
  • Celiac disease testing – for antibodies.

On the final page we look at the available treatments for diarrhea and ways in which to prevent it occurring.


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Treatments for diarrhea

Mild cases of acute diarrhea may be self-limiting and resolve without treatment. For underlying causes, particularly those leading to persistent or chronic diarrhea, these will be diagnosed and treated in addition to the symptom of diarrhea.

For all cases of diarrhea, the first important step in treatment is to rehydrate:3,4,9

Correcting dehydration is the first priority of treatment.

  • Replace lost fluids through measures ranging from drinking more fluids to receiving them intravenously in severe cases. Children and older people are more vulnerable to dehydration
  • Oral rehydration solution/salts (ORS) – water containing salt and glucose absorbed by the small intestine to replace the water and electrolytes lost in the watery feces. (In developing countries, ORS costs just a few cents, and the World Health Organization says ORS can safely and effectively treat over 90% of cases of non-severe diarrhea.) The recommended preparation of the solution is 75 mEq/l of sodium and 75 mmol/l of glucose
  • Oral rehydration products are available commercially – for example, Oralyte, Rehydralyte.

Zinc supplementation with a daily dose of 10 to 20 milligrams may reduce the severity and duration of diarrhea in children. The zinc supplement is recommended for 10 to 14 days, and it can help to reduce subsequent episodes of diarrhea in the child for 2 to 3 months.3

Over-the-counter antidiarrheal medicines are available:6

  • Loperamide (Imodium, for example) is an antimotility drug that reduces stool passage. Two tablets are taken after the first loose stool, one tablet after each subsequent loose stool12
  • Bismuth subsalicylate (for example, Pepto-Bismol) reduces diarrheal stool output in adults and children, and may be a safer alternative to loperamide. This drug can also be used as prophylaxis against traveler’s diarrhea.12

There is mixed advice that antidiarrheal medications could prolong bacterial infection by reducing excretion of pathogens via stools.6,10

Antibiotic treatment is reserved for cases of diarrhea that have been confirmed as caused by a bacterial infection. If the cause is medication, meanwhile, a review will be undertaken and switch to another drug if appropriate.9


Nutritionists from Stanford Health Care offer some nutritional tips for diarrhea, including, to stay hydrated:13

Bananas are high in potassium.

  • Sip on clear, still liquids such as fruit juice without added sugar, replacing lost water after each loose stool with at least one cup of liquid
  • Do most of the drinking between, not during meals when they may otherwise increase passage of food in the gut
  • Use high-potassium foods and liquids – examples include diluted fruit juices, potatoes (without the skin), bananas
  • Use high-sodium foods and liquids – broths, soups, sports drinks, salted crackers, and so on.

Other advice from the nutritionists is to:13

  • Eat foods high in soluble fiber to help thicken the stool – bananas, rice, oatmeal, for example
  • Limit certain foods that may make the diarrhea worse – such as creamy, fried and sugary foods
  • Add a probiotic.

The diet may make diarrhea worse – avoid caffeine contained in coffee, tea, soft drinks such as cola, and some over-the-counter headache remedies. Other aggravating elements of the diet include:10

  • Sugar-free gum, mints, sweet cherries, prunes
  • Fructose in high amounts, from fruit juices, grapes, honey, dates, nuts, figs, soft drinks and prunes
  • Lactose in dairy products
  • Magnesium
  • Olestra (Olean), a fat substitute.


There is mixed evidence for the role of probiotics for people with diarrhea, but there is thought to be an effect on the immune system. In children, there is evidence of benefit in reducing diarrheal illness duration by one day.6

Probiotics may have some prophylactic effect against traveler’s diarrhea12

Antibiotic-associated diarrhea may be reduced by the use of probiotics, as may diarrhea related to Clostridium difficile, although the evidence is mixed. Advice from the doctor is recommended since there are numerous strains, but the most studied for antibiotic-associated diarrhea are probiotics based on Lactobacillus rhamnosus and Saccharomyces boulardii.14

Probiotics to help with Clostridium difficile and antibiotic diarrheas were subjected to a randomized, controlled trial published in The Lancet, which found “no evidence” that a multistrain preparation of the bacteria was
effective in prevention of these conditions, calling for a better understanding of the development of antibiotic-associated diarrhea.15

Probiotics are available in capsules, tablets, powders and liquids.14

Prevention of diarrhea

In developing countries, prevention of diarrhea may be more challenging – here, there may be dirty water and poor sanitation. The following practical measures help to prevent the condition:3,4,6

  • Safe drinking water
  • Good sanitation (toilets and sewerage, for example)
  • Hand washing with soap – after defecation, after cleaning a child who has defecated, after disposing of a child’s
    stool, before preparing food, and before eating
  • For mothers with young babies, breastfeeding for the first 6 months of life
  • Good hygiene practices – both personal hygiene and in the kitchen
  • Education on the spread of infections.

There is evidence that interventions from public health bodies to simply promote hand washing can cut diarrhea rates by about a third.6

Vaccine prevention

Rotavirus vaccination helps to prevent diarrheal disease – in the US it is available for infants under the brand names RotaTeq and Rotarix.4,16

Giving children the measles immunization can substantially cut rates and severity of diarrheal diseases, and other vaccines have been researched against other infections.2

Developments about diarrhea in MNT news

Travelers taking antibiotics may be helping spread of ‘superbugs’

Travelers who use antibiotics are putting themselves and others at further risk, said researchers publishing in January 2015.

Amoxicillin use linked to diarrhea and thrush

A systematic review in November 2014 found that common antibiotics amoxicillin and amoxicillin-clavulanic acid can result in diarrhea and candidiasis/thrush.

Quarter of health care workers carry diarrhea spores on their hands

This January 2014 study found that around 1 in 4 health care workers’ hands were contaminated with Clostridium difficile spores after they had been carrying out routine care on infected patients.